docs: def crop(self, start_timestamp, end_timestamp):
          """
          Return a new TimeSeries object contains all the timstamps and values within
          the specified range.
  
          :param int start_timestamp: the start timestamp value
          :param int end_timestamp: the end timestamp value
          :return: :class:`TimeSeries` object.
          """
          output = {}
          for key, value in self.items():
              if key >= start_timestamp and key <= end_timestamp:
                  output[key] = value
  
          if output:
              return TimeSeries(output)
          else:
              raise ValueError('TimeSeries data was empty or invalid.')